Surface engineering of MXene quantum dots for the designing of optical metal sensors

Background: One of the newly developed two-dimensional (2D) materials, MXenes Quantum dots (MQDs) has become a hot topic in materials science over the past ten years. Their potential in fluorescent sensing applications has also gained a lot of attention after the recognition of their distinctive features. Aim of review: The review signifies the understanding of the synthesis, mechanism, and surface engineering of MQDs for their application as fluorescence sensors. Findings: The MQDs are prepared by simple top-bottom, bottom-up, and advanced microwave approaches. The mechanism is based on quenching which involves Forster Resonance Energy Transfer (FRET), Inner Filter Effect (IFE), or Photo Induced Electron Transfer (PET) in a broad range of sensing applications. However, sometimes a new analyte is added to recover the fluorescence quenching. Doping with a heteroatom (N, P, S or metal atoms) and co-doping (N-P, N-S, N-, Pt, etc.) has been frequently used to overcome the drawbacks of MQDs such as aggregation, oxidation, and low quantum yield. MQDs modification can be realized by covalent bonding, aryl diazonium chemistry, or non-covalent interactions. Moreover, surface defects are removed to enhance the Photoluminescence Quantum Yield (PLQY) by passivation. However, overcoming the challenges of MQDs synthesis restricted to Ti, detail sensing mechanistic study, and advancement in surface engineering (modification and passivation) could lead to future highly efficient and vast MQDs sensors applications.